The methods for this are really interesting. I wonder if you could estimate loss rates (death/predation) by identifying a number of fish going upstream, then use the downstream data to roughly see the number lost based on identified fish that never came back down. Although I guess this could be done with the up/down data. Would be interesting to see the data after a number of spawning seasons, well done to the team working on it. If the biologist is looking for seasonal workers for this I will have to keep it in mind for when I move out there.
